forked from xuos/xiuos
118 lines
2.8 KiB
C
118 lines
2.8 KiB
C
/* Copyright JS Foundation and other contributors, http://js.foundation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* This file is based on work under the following copyright and permission
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* notice:
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*
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunSoft, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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*
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* @(#)s_tanh.c 1.3 95/01/18
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*/
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#include "jerry-math-internal.h"
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/* tanh(x)
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* Return the Hyperbolic Tangent of x
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*
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* Method:
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* x -x
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* e - e
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* 0. tanh(x) is defined to be -----------
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* x -x
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* e + e
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*
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* 1. reduce x to non-negative by tanh(-x) = -tanh(x).
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* 2. 0 <= x <= 2**-55 : tanh(x) := x * (one + x)
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*
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* -t
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* 2**-55 < x <= 1 : tanh(x) := -----; t = expm1(-2x)
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* t + 2
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*
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* 2
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* 1 <= x <= 22.0 : tanh(x) := 1- ----- ; t = expm1(2x)
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* t + 2
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*
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* 22.0 < x <= INF : tanh(x) := 1.
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*
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* Special cases:
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* tanh(NaN) is NaN;
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* only tanh(0) = 0 is exact for finite x.
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*/
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#define one 1.0
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#define two 2.0
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#define tiny 1.0e-300
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double
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tanh (double x)
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{
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double t, z;
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int jx, ix;
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/* High word of |x|. */
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jx = __HI (x);
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ix = jx & 0x7fffffff;
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/* x is INF or NaN */
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if (ix >= 0x7ff00000)
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{
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if (jx >= 0)
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{
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/* tanh(+-inf) = +-1 */
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return one / x + one;
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}
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else
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{
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/* tanh(NaN) = NaN */
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return one / x - one;
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}
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}
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/* |x| < 22 */
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if (ix < 0x40360000)
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{
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/* |x| < 2**-55 */
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if (ix < 0x3c800000)
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{
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/* tanh(small) = small */
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return x * (one + x);
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}
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if (ix >= 0x3ff00000)
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{
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/* |x| >= 1 */
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t = expm1 (two * fabs (x));
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z = one - two / (t + two);
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}
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else
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{
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t = expm1 (-two * fabs (x));
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z = -t / (t + two);
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}
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}
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else
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{
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/* |x| > 22, return +-1 */
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z = one - tiny; /* raised inexact flag */
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}
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return (jx >= 0) ? z : -z;
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} /* tanh */
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#undef one
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#undef two
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#undef tiny
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